Direct injection (DI) engines may produce more soot than port fuel injected engines in part due to diffuse flame propagation. As a consequence of diffuse flame propagation, fuel may not adequately mix with air prior to combustion, resulting in pockets of rich combustion that generate soot. Further, DI engines may be susceptible to generating soot during high load and/or high speed conditions when there is a lack of sufficient air and fuel mixing.
The inventors herein have recognized various issues in applying particulate filters to DI, spark-ignition engines. For example, it can be difficult to maintain accurate emission control during particulate filter regeneration in a DI, spark-ignition engine.
Thus, methods and systems for controlling operation of exhaust of an engine including a particulate filter are described. One example method includes generating compressed air during engine operation and storing the compressed air. Thus, the method may include, during or after engine shutdown, pushing the compressed air through the particulate filter using a pressure of the compressed air.
By performing a particulate filter regeneration during and/or after engine shutdown, the particulate filter can be regenerated by an increased flow of oxygen to the particulate filter while avoiding potential increased emissions from a three-way catalyst in an exhaust tailpipe.
In one example, the method may include pushing compressed air through the particulate filter in a direction that is the same direction as exhaust flow during engine combustion. In this way, it may be possible maintain more commonality in control between engine running and engine shutdown regenerations.
Also, if an engine running regeneration (e.g., during engine combustion) is carried out when engine shutdown is requested, the particulate filter regeneration can be continued through engine shutdown conditions without changes in a direction of airflow at the particulate filter.
Yet another potential advantage of regenerating the filter during and/or after engine shutdown using stored compressed air is that a regeneration reaction can be delayed or advanced to a time when particulate filter conditions are appropriate for carrying out the regeneration reaction. For example, compressed air may be stored until the particulate filter temperature becomes hot enough to carry out the regeneration reaction. Further still, particulate filter regeneration may be selectively carried out under particular engine shutdown conditions (e.g., shutdowns in which filter regeneration is already commenced during engine running conditions, or shutdowns in which filter temperature is high enough), and not during others.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.